Growth hormone (GH) responses to agents that perturb the hypothalamic growth hormone axis have been widely used in psychiatric research as a peripheral correlate of central noradrenergic activity. "Blunted" GH-responses to clonidine are generally attributed to post-synaptic noradrenergic receptor down-regulation. In addition to clonidine, we have administered growth hormone-releasing factor (GRF), caffeine, glucose, yohimbine, and TRH to panic disorder patients and normal control subjects. Overall, patients with panic disorder appear to have decreased GH function using a wide array of stimuli that activate the hypothalamic-GH axis. Future studies will investigate the GH response to sleep, exercise, pentagastrin, CI-988, and pyridostigmine.